Multi-mode heat transfer using a thermal heat pipe valve

ABSTRACT

An electronic device has a heat pipe containing a heat transfer fluid. The heat pipe has a first section and a second section. Inside the heat pipe is a valve disposed between the first section and second section of the heat pipe. The valve has an actuator that is used to regulate the flow of the heat transfer fluid between the first section and the second section of the heat pipe in response to a changed state detected by a sensor.

FIELD OF THE INVENTION

This invention relates to a heat transfer system. More specifically, itrelates to a multi-mode heat transfer system having a valve disposedbetween two sections of a heat pipe for use in electronic devices.

BACKGROUND OF THE INVENTION

The trend in the design of electronic devices, such as notebookcomputers or personal data assistants, is to provide as small a packageas functionally possible while at the same time providing forcomfortable cool and lightweight operation. Additionally, market forcesalso require that electronic devices, such as notebook computers,deliver the same computational horsepower as their desktop equivalentsin order to justify their cost. However, to achieve this fasterperformance, integrated circuits (ICs), especially the centralprocessing unit (CPU), the graphics controller, and the memory devicesall require more power, which create more heat in the device. Thecombination of this additional heat and a smaller package createsadditional stress on the internal components, causing the electronicdevices to quit working or literally become too hot to handle.

Another problem, especially with notebooks, is that peripheral modulessuch as floppy, CD-ROM, Zip and DVD drives and PC cards not only take upspace, they create more heat. Also, many of these peripheral modules aresensitive to heat generated from the other components in the electronicdevice and may prematurely fail to operate if these temperaturesensitive modules become too hot.

Several different techniques have been developed to deal with the excessheat generated in an electronic device. By slowing the CPU clock ratedown, the heat generated by the CPU decreases; however, the user'sdesire for desktop performance can not be met. By creating a dockingstation to hold various peripherals that are not used when theelectronic device is mobile, more space becomes available in theelectronic device for additional heat transfer structures. However, theelectronic device in a docking environment usually causes the user tochange their expectations of use such that the user wants fullperformance with an external monitor and keyboard as well as access to anetwork such as the Internet. In this situation, usually the electronicdevice's cover or lid is closed, or the electronic device is enclosed bythe docking station, and in both cases the heat transfer properties ofthe electronic device change. What is required for future electronicdevices is an optimal way to keep them cool in whatever operating modethe user decides to use.

SUMMARY OF THE DISCLOSURE

An electronic device has a heat pipe containing a heat transfer fluid.The heat pipe has a first section and a second section. Inside the heatpipe is a valve disposed between the first section and second section ofthe heat pipe. The valve has an actuator that is used to regulate theflow of the heat transfer fluid between the first section and the secondsection of the heat pipe in response to a changed state detected by asensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a heat transfer system for anelectronic device.

FIG. 2 illustrates the inner workings of the preferred embodiment of aheat pipe valve in a normally open configuration.

FIG. 3A shows the cross-sectional view taken from the AA section of FIG.2.

FIG. 3B shows the cross-sectional view taken from the BB section of FIG.2.

FIG. 3C shows the cross-sectional view taken from the CC section of FIG.2.

FIG. 4 illustrates the inner working of a first alternative embodimentof a heat pipe valve in a normally closed configuration.

FIG. 5 illustrates the inner workings of a second alternative embodimentof a heat pipe valve in a normally closed configuration.

FIG. 6 illustrates the inner workings of a third alternative embodimentof a heat pipe valve which uses a magnetic actuator and a magneticallyattractive screen.

FIG. 7 illustrates the inner workings of a fourth alternative embodimentof a heat pipe valve which uses two coils to control the position of theactuator.

FIG. 8 is a flow chart of an exemplary embodiment of the logic used inlogic circuit 80 to determine when to open/close the heat pipe valve andturn on/off the fan for a notebook computer.

DETAILED DESCRIPTION OF THE PREFERRED AND ALTERNATIVE EMBODIMENTS

FIG. 1 is a schematic illustration of a heat transfer system 10 for anelectronic device 12, such as a notebook computer or personal dataassistant (PDA), comprised of at least one heat producing component 40which is attached to a second heat pipe section 180 which carries heatfrom the component 40 to a heat sink area 50. A heat pipe is a passivehermetically sealed closed container which contains a wick or othercapillary structure, contained within the inner walls of the container,soaked with a small amount of vaporizable fluid, preferably water oranother liquid that has been depressurized to reduce the boiling pointof the fluid to a temperature less than the maximum operatingtemperature of the heat producing component 40, i.e. 90° C. Unlessspecifically called out, the term fluid used in this specificationencompasses the fluid within the heat pipe in either a liquid or vaporstate. In the preferred embodiment, the heat producing component 40applies heat to one end of the heat pipe causing the water or otherliquid to vaporize (boil) and thus absorb energy, then this vaportravels to the cool end of the heat pipe and condenses. In the processof condensation, the fluid releases the heat (the energy previouslyabsorbed) to the exterior of the heat pipe. The fluid returns to thewarm portion of the pipe via the wick or other capillary structure andthe process is repeated. As the vapor pressure drop between theevaporator and condenser is very small, the heat pipe maintains anessentially constant temperature along the length of the heat pipe. Withthe proper design, the heat pipe can transfer large amounts of heatwithout temperature losses.

Heat sink area 50 is designed to radiate heat freely into the air awayfrom the electronic device 12. Optionally, to improve the rate of heattransfer, a fan 60 may be combined with heat sink area 50. The fan 60 iscontrolled by logic circuit 80 to operate depending on the states ofseveral factors, as will be discussed in more detail later. Exemplaryfactors are: sensing when the component 40 is too hot; sensing thatambient air inside the electronic device 12 is too hot; sensing that theelectronic device 12 is being used in different modes (such as docking);sensing that the lid of the electronic device 12 has been closed;sensing that a new temperature sensitive module has been inserted intothe electronic device 12; and detecting that a component, such as anintegrated circuit (IC), has changed to a new mode of operation (i.e., aCPU speedup or a change of the graphic controller display mode). Thoseskilled in the art will appreciate that other states that affect thethermal performance of the electronic device 12 could be used to provideinput to logic circuit 80 and still fall with the spirit and scope ofthe invention.

There may be times during operation of the electronic device 12, such asin a notebook computer, when nominal heat dissipation is required andfan operation is not desired due to the noise created or the powerconsumed by the fan. In these instances, a heat spreader 30 is coupledto component 40 through a first heat pipe section 170 and is placedunder the keyboard, palmrest or other exposed surface area to allow heatto be released out of the electronic device 12. However, this heatspreader 30 often spreads heat to temperature sensitive modules or otherperipheral devices, which may affect their performance. In addition,when the lid or cover is closed over the exposed surface area, it may benecessary for the heat spreader 30 to stop functioning, as the heat itis dissipating cannot leave the electronic device 12 and the excess heatbuilds up inside the electronic device 12 causing the temperaturesensitive modules to fail. Thus, the heat spreader 30 restricts thetemperature that the heat producing component 40 can operate. If theheat spreader 30 can be disconnected from the heat sink area 50 and fan60 circuit, the heat producing component 40 can be operated at highertemperatures that are within its specification without affecting thecomponents near the heat spreader 30.

The invention addresses this problem by creating a magnetic valve 20,which is disposed between the second heat pipe section 180, and thefirst heat pipe section 170. The second heat pipe section 180 is furthercoupled to component 40 and heat sink area 50 and first heat pipesection 170 is further coupled to heat spreader 30. This magnetic valve20 is electronically controlled by a driver 70 that is driven by a logiccircuit 80 which combines a number of decision variables fromtemperature control circuit 90, dock control circuit 100, andmiscellaneous control circuit 110. Temperature sensor(s) 120 providetemperature state(s) to temperature control circuit 90 in the form ofdifferent levels, which in turn impels the magnetic valve 20. Dockdetection circuit 130 provide docking states to dock control circuit 100in the form of different levels which impels the magnetic valveaccordingly to deal with different dock situations. Severalmiscellaneous sensors or switches such as lid switch 140, module detect150, or IC mode detect 160, among others, can be input into amiscellaneous control circuit 110 in the form of different levels. Thedifferent levels correspond to respective changed states, whichdetermine when to impel magnetic valve 20.

Also shown is a dock device 64, such as a docking station, which has anadditional fan 62 which can be used to couple additional airflow acrossheat sink area 50, which is exposed when docked, depending on the powerload of the electronic device 12 and the amount of heat detected in heatsystem 10.

FIG. 2 illustrates the preferred embodiment's cross section of magneticvalve 20 and its coupling to a second heat pipe section 180 and a firstheat pipe section 170. The magnetic valve 20 is comprised of a shell 22,which allows magnetic penetration through it, such as copper tubing thatalso provides excellent heat conduction. Surrounding the shell 22 is acoil 230 of wire which is wound preferably in a voice coil configurationto permit an electric current flowing through it to generate a magneticfield. The magnetic field may also be provided by an external magneticmaterial or other magnetic field producing device. When using a coil230, the magnetic field can be enhanced or prevented from radiating farfrom magnetic valve 20, by using an optional field concentrator 220,preferably a ferrous shield. Inside of magnetic valve 20 is placed anactuator 250, which may be either magnetically attractive, such as aferrite core, or magnetically polarized, such as a permanent magnet. Aspring 240 is used to position the actuator 250, which is shown in FIG.2 in a `normally open` position. Actuator 250 has a hollow center orgrooves on its peripheral surface to allow fluid in the magnetic valve20 to pass by the valve. A first wick 200 allows fluid to move throughfirst heat pipe section 170. A second screen 260 provides support forthe spring 240 and is perforated with at least one aperture to allowfluid and optionally, a second wick 190 from second heat pipe section180 to flow into the magnetic valve 20. When coil 230 is not activatedthe spring 240 retracts actuator 250 from a first screen 210 which hasat least one aperture designed to allow fluid to flow when actuator 250is not in contact with it. When coil 230 is activated, the magneticfield generated by the electronic current flowing through coil 230impels actuator 250 to contact first screen 210 and thus block off theat least one aperture to prevent fluid from flowing from second heatpipe section 180 to first heat pipe section 170. Although the fluid flowin the heat pipe is restricted from flowing to the first heat pipesection 170, a small amount of heat might be transmitted through themetal shell. Another embodiment envisions that an insulator is placedbetween the valve and metal shell of the first heat pipe section 170 toreduce this heat leakage. Another embodiment to reduce heat leakage isto have first screen 210 made of an heat insulating material.

Although first wick 200 and second wick 190 are shown as being placed inthe center of the heat pipe, other architectures for providing a wick orcapillary force are known to those skilled in the art and could be usedin place of that shown in the drawings and still fall within the spiritand scope of the invention.

It should be noted that actuator 250 and spring 240 should be orientedsuch that the spring 240 is in contact with the second screen 260, whichcontacts that heat pipe section attached to heat producing component 40.This selection of valve orientation prevents pressure built up in theheat pipe fluid from heat generated by heat producing component 40 fromcounteracting the spring compression force of spring 240 when closed andthereby cause a fluid leak in magnetic valve 20.

FIG. 3A illustrates a view of the cross-section AA perspective of FIG. 2of first screen 210. Aperture 212 provides openings for fluid flow andtarget 214 provides a stop.

FIG. 3B illustrates the cross-sectional view from the BB perspective ofactuator 250, showing actuator aperture 252, which allows fluid flowthrough the actuator.

FIG. 3C illustrates the cross-sectional view from the CC perspective ofFIG. 2 of the second screen 260. Second screen 260 has aperture 262 andcenter aperture 264 that allows second wick 190 to enter the magneticvalve 20.

Those skilled in the art will appreciate that other aperture shapes arepossible for the screens and actuator and still meet the spirit andscope of the invention.

FIG. 4 illustrates a first alternative embodiment of a normally closedvalve 20 in which spring 242 is long enough to force actuator 250 upagainst first screen 210, effectively blocking the flow of fluid throughthe apertures in first screen 210. The coil 230 and field concentrator220 are shifted over the spring 242 such that when coil 230 isactivated, the magnetic field generated impels actuator 250 towardsecond screen 260 thereby compressing spring 242 and allowing fluid toflow through first screen 210.

FIG. 5 illustrates a second alternative embodiment of valve 20 in whichan actuator 258 is shaped to fit into the aperture of first screen 210such that the amount of displacement of the actuator 258 from firstscreen 210 is proportional to the amount of electric current in coil 230and the displacement of the actuator 258 controls the volume of fluidflow through first screen 210. This approach allows a controlled variedfluid flow that further refines the amount of heat transferred to firstheat pipe section 170. An opening 252 in actuator 258 provides a fluidpath through actuator 258. Optionally, to maintain tight control offluid seepage around actuator 258, a lubricating film 254, preferably aTeflon lubricant like polytetrafluoroethylene (PTFE), is applied on theoutside of actuator 258. Wick 190 can be placed in actuator 258 to helpcontrol the fluid flow from the second heat pipe section 180.

FIG. 6 illustrates a third alternative embodiment of the invention inwhich actuator 259 is comprised of a magnetic material and a secondscreen 262 is comprised of a magnetically attractive material such asiron. In this instance, there is no need for a spring as actuator 259returns to an open position upon deactivation of the magnetic field fromcoil 230, due to the actuator's magnetic attraction to second screen262. A lubricating film 254, preferably PTFE, allows the actuator 259 tosmoothly slide back and forth within the shell 22. Coil 230 and fieldconcentrator 220 (if used) are positioned over first screen 210 to drawand impel actuator 259 towards first screen 210 when coil 230 isenergized with electrical current to create a magnetic field.

FIG. 7 illustrates a fourth alternative embodiment of the invention inwhich the actuator is comprised of either a magnetic material ormagnetically attractive material. Two coils, a first coil 230A and asecond coil 230B are used to each attract actuator 250, such that byactivating either the first coil 230A or the second coil 230B, the valveis closed or opened, respectively. It is also envisioned in anotherembodiment that once the valve is closed by having first coil 230Aactivated and impelling actuator 250 to abut against first screen 210and after a sufficient time for the vapor pressure in second heat pipesection 180 to build up, the electric current in first coil 230A can bereduced or shut-off and the valve held closed by the pressure in secondheat pipe section 180. This reduction or shut-off of current into firstcoil 230A allows for reduced power consumption. As second heat pipesection 180 cools, either due to reduced power from heat producingcomponent 40 or due to the effectiveness of fan 60 or dock fan 62 andheat sink area 50, the pressure on actuator 250 is reduced and vaporflows into the first heat pipe section 170. As the heat spreader 30 thenwarms, logic circuit 80 detects when to re-activate first coil 230A toclose the heat pipe valve. The magnetic fields in first coil 230A andsecond coil 230B are optionally enhanced with a first field concentrator220A and second field concentrator 220B, respectively. In anotherembodiment, it is envisioned that first coil 230A and second coil 230Bare used to sense the location of actuator 250 before determining whichcoil to activate to impel actuator 250 to an open or closed position.This sensing is performed by detecting the change in inductance of therespective coil, which can be accomplished by various techniques knownto those skilled in the art. By determining the position of actuator250, if the electronic device 12 is jarred or moved, the valve couldmove out of position, be detected, and returned back to its properstate. It is also envisioned that the energizing current into the coilscan optionally be pulsed to a higher level to overcome either initialfriction or magnetic forces and then reduced to maintain the valve in anopen or closed position. This variable pulsed energizing currenttechnique allows for smaller coils thus reducing cost and saving space.

FIG. 8 is a flow chart representing an exemplary embodiment of logiccircuit 80 for an electronic device, such as a notebook computer, wherethe heat spreader is used as the primary heat dissipation and the heatsink area and fan used when either the heat spreader is overloaded orthe electronic device is being used in a mode where the use of the heatspreader is undesirable, such as when the cover is closed. Start block400 defines the initial state of the logic circuit 80, where a valve isinitially open to allow the heat spreader to operate and the fan is offto conserve power. Logic circuit 80 checks miscellaneous control circuit110 to determine if the lid is closed in decision block 410. If the lidis closed the logic proceeds to decision block 470 because the heatspreader will be unable to dissipate heat readily from the electronicdevice. Otherwise, logic circuit 80 checks dock control circuit 100 indecision block 420 to see if the electronic device 12 is docked. Ifdocked, the electronic device receives power from an AC outlet and thefan can be used without regard to power dissipated from the fan so thelogic proceeds to decision block 470. Otherwise, logic circuit 80 checksmiscellaneous control circuit 110 in decision block 430 to see if atemperature sensitive module, like a battery or a peripheral such as afloppy drive, CD-ROM or DVD player, is installed in the electronicdevice. When a temperature sensitive module is installed, the heatspreader may cause it to become too warm so the logic proceeds todecision block 470. Otherwise, logic circuit 80 checks to see if the CPU(the heat producing component 40 in this example) is running in a highpower mode in decision block 440. If so, the logic proceeds to decisionblock 470 because in this example the heat spreader will be unable tohandle dissipating the heat from the CPU. Otherwise, logic circuit 80checks temperature control circuit 90 to see if the heat spreader 30 hasreached its maximum operating temperature in decision block 450. If ithas (perhaps from a combination of other factors such as graphics mode,memory operation, or PC cards), then the logic proceeds to decisionblock 490. Otherwise, the magnetic valve 20 is opened in block 460 toallow heat flow from component 40 (here represented as a CPU) to theheat spreader 30 and the logic begins checking at block 410 again.

Decision block 470 compares the ambient temperature in the electronicdevice to a preset temperature limit. If the preset temperature limithas been reached, block 490 enables the fan 60 to turn on and cool heatsink area 50 and block 490 closes the magnetic valve 20 and the logicproceeds back to start block 400. Otherwise, if the ambient temperatureis O.K., the fan 60 is turned off in block 480 before proceeding back tothe start block 400.

Those skilled in the art will appreciate that other logicimplementations exist other than that shown in the exemplary embodimentto control the magnetic valve 20 and fan 60 and still fall within thescope and spirit of the invention. For example, alternative embodimentshave been contemplated where different subsets of the decision blocks410-440 are present. Indeed, one of these alternate embodimentseliminates all of the decision blocks 410-440 and 470-480, with startblock 400 connected directly to block 450 and having block 490 onlyclosing the valve.

What is claimed is:
 1. An electronic device having a multi-mode heattransfer apparatus, comprising:a heat spreader; a heat sink area; a heatpipe containing a heat transfer fluid, said heat pipe having a firstsection and a second section, said first section coupled to said heatspreader, said second section coupled to said heat sink area; a valvedisposed in said heat pipe between said first section and said secondsection of said heat pipe, said valve further comprising an actuator,said actuator used to regulate a flow of said heat transfer fluidbetween said first section and said second section of said heat pipe;andat least one sensor, said at least one sensor detecting at least onechanged state; and at least one logic circuit coupled to said at leastone sensor, said at least one logic circuit impelling said actuator ofsaid valve in response to said at least one changed state.
 2. Theelectronic device of claim 1, further comprising a first screen, saidfirst screen disposed between said first section and said second sectionof said heat pipe, said first screen having at least one aperture,wherein said at least one aperture is closed when said actuator isimpelled to abut against said first screen, thereby restricting the flowof said heat transfer fluid between said first section and said secondsection of said heat pipe.
 3. The electronic device of claim 2, whereinsaid first screen is comprised of a thermally isolating material.
 4. Theelectronic device of claim 2, further comprising a second screen, saidsecond screen disposed between said actuator and said second section ofsaid heat pipe, said second screen having at least one aperture, whereinsaid at least one aperture permits the flow of said heat transfer fluidand wherein said second screen is comprised of a magnetically attractivematerial.
 5. The electronic device of claim 4, wherein said actuator isformed of a magnetically attractive material and said valve furthercomprises a spring, said spring disposed between said actuator and saidsecond screen.
 6. The electronic device of claim 4, wherein saidactuator is formed of permanent magnetic material.
 7. The electronicdevice of claim 1, wherein said actuator is coated with a lubricatingmaterial.
 8. The electronic device of claim 1, wherein said at least onelogic circuit produces an electric current and the electronic devicefurther comprising at least one coil surrounding said heat pipe, said atleast one coil coupled to said at least one logic circuit, whereby saidat least one coil produces a magnetic field when said electric currentfrom said at least one logic circuit is supplied to said at least onecoil, and wherein said magnetic field passes through said heat pipeimpelling said actuator of said valve.
 9. The electronic device of claim8, wherein said at least one coil further comprises a field concentratorcircumscribing said at least one coil whereby said field concentratorenhances said magnetic field within said heat pipe.
 10. The electronicdevice of claim 8, wherein said flow of heat transfer fluid between saidfirst section and said second section of said heat pipe is proportionalto the amount of said electric current supplied to said at least onecoil.
 11. The electronic device of claim 1, wherein said heat sink areafurther comprises a fan, said fan coupled to said at least one logiccircuit and wherein said fan cools said heat sink area when activated bysaid at least one logic circuit.
 12. The electronic device of claim 1,further comprising:a docking station, said docking station furthercomprising a dock fan; and said heat sink area exposed to allow saiddock fan from said docking station to couple air between said heat sinkarea and said docking station.
 13. The electronic device of claim 12,wherein said at least one sensor further comprises:a docking sensor,said docking sensor detecting a docking state; and wherein said at leastone logic circuit is coupled to said docking sensor, said at least onelogic circuit impelling said actuator of said valve in response todetection of said docking state by said docking sensor.
 14. Theelectronic device of claim 1, wherein said at least one sensor furthercomprises:a temperature sensor, said temperature sensor detecting atemperature state; and wherein said at least one logic circuit iscoupled to said temperature sensor, said at least one logic circuitimpelling said actuator of said valve in response to detection of saidtemperature state by said temperature sensor.
 15. The electronic deviceof claim 1, wherein said valve is normally closed when said actuator isnot impelled by said at least one logic circuit and wherein said valveis opened when said actuator is impelled by said at least one logiccircuit.
 16. The electronic device of claim 1, wherein said valve isnormally open when said actuator is not impelled by said at least onelogic circuit and wherein said valve is closed when said actuator isimpelled by said at least one logic circuit.
 17. An electronic devicecomprising:a valve having a shell with a first end and a second end; afirst heat pipe coupled to said first end of said shell of said valve; asecond heat pipe coupled to said second end of said shell of said valve.at least one heat producing component, said component coupled to saidfirst heat pipe; a heat sink area, said heat sink area coupled to saidsecond heat pipe; a heat spreader, said heat spreader coupled to saidfirst heat pipe; and at least one control circuit, said at least onecontrol circuit having at least one sensor, said at least one controlcircuit actuating said valve to couple said heat transfer fluid betweensaid first heat pipe and said second heat pipe in response to said atleast one sensor.
 18. A method for cooling an electronic device,comprising the steps of:detecting a first changed state thereby creatinga first signal having a first level and a second level; opening a valvedisposed in a heat pipe between a first section attached to a heatspreader and a second section attached to a heat sink area in responseto said first level of said first signal; and closing said valve inresponse to said second level of said first signal.
 19. The method ofclaim 18, wherein the step of detecting said first changed state furthercomprises the step of detecting an event selected from the groupconsisting of a lid closure state, a dock state, a temperature sensitivemodule present state, a mode change state and a temperature state. 20.The method of claim 18, further comprising the steps of:detecting asecond changed state thereby creating a second signal having a firstlevel and a second level; enabling a fan to couple air across said heatsink area in response to said first level of said second signal; anddisabling said fan in response to said second level of said secondsignal.
 21. The method of claim 20 wherein the step of detecting saidsecond changed state further comprises the step of detecting an eventselected from the group consisting of a lid closure state, a dock state,a temperature sensitive module present state, a mode change state and atemperature state.
 22. The method of claim 18 wherein said valve furthercomprises a shell enclosing an actuator and wherein closing said valvefurther comprises the step of applying an electrical current to a coilthereby creating a magnetic field wherein said magnetic field impelssaid actuator.
 23. The method of claim 18 wherein said valve furthercomprises a shell enclosing an actuator and wherein said closing saidvalve further comprises the step of disabling an electrical current to acoil thereby eliminating a magnetic field that counteracts a forceacting on said actuator thereby causing said actuator to be impelled bysaid force.
 24. The method of claim 18, wherein said valve furthercomprises a shell enclosing an actuator and further comprising the stepof thermally isolating said shell from said first section of said heatpipe.
 25. An electronic device using the method of claim 18.